This invention relates to an improved battery jar and method of making same. More specifically this invention relates to improved battery jars for mobile vehicles.
In the past, battery jars have been made of a number of different substances and by a number of different techniques. Thus battery jars have been formed of rubber, glass or insulated steel. More recently plastic materials have been utilized to produce reliable and lightweight battery jars. One conventional method of making plastic jars has been by the rotational molding process. Although the performance and the cost of these plastic jars have been more favorable than that of former constructions, the rotational molding process does not provide completely satisfactory dimensional control and has not been capable of handling materials such as polypropylene and low-melt index, high molecular weight polyethylene. Further, the rotational molding process requires substantial time and personnel and is quite sensitive to variations in the operation of the mold by an operator.
Plastic battery jars have also been formed in a single step by an injection molding process. One drawback, however, to forming certain types of battery jars, such as, elongated battery jars, in a single piece with an injection molding process is that the long flow path from the injection point at the bottom of the jar to the top thereof makes it necessary to have greater wall thickness thereby using more material per jar. In addition, the jar walls have a considerable "draft" from the bottom to the top in order to provide a successful mold. This despite the fact that it is desirable to have the opposing side walls of the jar parallel and of uniform thickness in order to make a tight pack of the battery plates inside of the jar from the bottom to the top thereof. Still another drawback is that with respect to jars used in moving vehicles, i.e., motive battery jars, there are approximately 40 different sizes required for the various batteries made. Since a different mold is required for almost every size variation, the cost of the molds for forming a complete line of such battery jars is enormous. In addition, the production costs are increased since molds must be changed very frequently in order to supply all sizes or in the alternative large numbers of bulky battery jars must be inventoried. Finally, in prior art injection molding processes, extra steps were required in order to form handles, edges for supporting the battery plates, etc., on the side walls of the battery jars.
It is accordingly an object of the present invention to provide an improved plastic battery jar.
It is another object of the present invention to provide an improved method of making plastic battery jars.